How to validate an input as an number in JavaScript

Question

I'm new with JavaScript programming and have been trying to validate a number that is inputted from a user on a php page. Here is the javascript that is included.

var validate_and_create = function(){
    var i_number = $("input_number").value;
    var isValid = true;

    if (i_number === ""){
        $("create_n_error").firstChild.nodeValue = "Number text field cannot be blank.";
        isValid = false;
    } else {
        if  (typeof i_number === 'number') {
            $("create_n_error").firstChild.nodeValue = "This is a number!";
            isValid = true;
        } else {
            $("create_n_error").firstChild.nodeValue = "This is not a number!";
            isValid = false;
        }
    }

It always prints that the input is not a number even when integer values are inserted in the textbox. So I'm sure its taking the input as a string input. So do I have to convert it to integer so I can validate? or am I doing something wrong?

An inputs value is always of type string, you should be using isNaN to check for numeric values. — adeneo
– adeneo, Commented Mar 10, 2016 at 21:33
You might be better off using a regular expression to validate your input, depending on what you want to allow. — Dave
– Dave, Commented Mar 10, 2016 at 21:35
Possible duplicate of Is there a (built-in) way in JavaScript to check if a string is a valid number? — Heretic Monkey
– Heretic Monkey, Commented Mar 10, 2016 at 21:52
why not use the html5 type=number? The browser will take care of the validation and mobile users should get the correct, numeric, keyboard automatically — Pevara
– Pevara, Commented Mar 11, 2016 at 16:02

Borys Serebrov · Accepted Answer · 2016-03-10 21:48:59Z

1

You can use parseInt to convert the value to integer, like parseInt("55", 10) will return 55.

And something like parseInt("xx",10) returns NaN.

answered Mar 10, 2016 at 21:48

Borys Serebrov

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Comments

Enrique Padilla · Accepted Answer · 2016-03-11 15:56:49Z

0

Thanks adeneo, isNaN works for validation.

Code below:

var validate_and_create = function(){
    var i_number = $("input_number").value;
    var isValid = true;

    if (i_number === ""){
        $("create_n_error").firstChild.nodeValue = "Number text field cannot be blank.";
        isValid = false;
    } else {
        if  (isNaN(i_number)) {
            $("create_n_error").firstChild.nodeValue = "This is not a number!";
            isValid = false;
        } else {
            $("create_n_error").firstChild.nodeValue = "This is a number!";
            isValid = true;
        }
    }

edited Mar 11, 2016 at 15:56

answered Mar 11, 2016 at 15:49

Enrique Padilla

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